1. Field of the Invention
The present invention relates to a protection circuit applied to an AC power source and a related protection method thereof, and particularly to a protection circuit and a protection method that can prevent from misjudging that the AC power source is not turned off when the AC power source is one-line off, resulting in an X capacitor not being discharged in time.
2. Description of the Prior Art
In order to prevent a user from suffering an electric shock when the user touches an electronic device, a circuit safety specification defines that an X capacitor (X-cap) needs to be connected to a discharge resistor in parallel so that a voltage stored in the X capacitor can be discharged to be lower than a safety voltage within a predetermined time when the electronic device is turned off. When the electronic device is turned off, the prior art sometimes only makes an alternating current (AC) power source coupled to the electronic device be one-line off due to consideration of lowering cost of the electronic device (e.g. an N line of the AC power source is one-line off).
However, when the N line of the AC power source AC is one-line off, because an L line of the AC power source still has high impedance, there are not greater difference between a peak value of a direct current (DC) voltage of a high voltage pin of the electronic device coupled to the X capacitor corresponding to the L line of the AC power source and a peak value of the DC voltage of the high voltage pin corresponding to the N line of the AC power source, resulting in the prior art misjudges that the AC power source is not turned off. Therefore, the prior art applied to single open-circuit of the AC power source is not a good choice for the user.